Generally, “porous materials”, which refer to materials with a pore volume of 10 to 98% based on the total volume, have properties such as impact energy absorption capability, gas and liquid permeability, sound shield, low thermal conductivity, electrical insulation and the like due to pores therein and thus, have been widely used as impact absorbing materials, filters, sound shielding materials, insulators and are also expected to be commercially utilized in more fields. Also, the porous materials are expected to be applied as a lightweight structure, a core material of sandwich structure and the like. Examples of porous metal and alloy materials known in the prior art include aluminum (Al), magnesium (Mg), zinc (Zn), iron (Fe), lead (Pb), gold (Au), silver (Ag), zirconium (Zr), copper (Cu), nickel (Ni), titanium (Ti), cobalt (Co), nickel-chromium (Ni—Cr) alloy and stainless steel and the like.
The porous metal and alloy materials are used in various fields. Specifically, examples of materials used as impact absorbing materials and structural materials include aluminum (Al), copper (Cu), Nickel (Ni) and the like, examples of materials used as filtering materials include copper (Cu), stainless steel, gold (Au) and Nickel (Ni) and examples of materials used as sound shielding materials include copper (Cu).
However, due to the demand for high performance and quality improvement in the aeronautics and space fields, the automobile fields, the industrial mechanical fields, the electrical and electronics fields, requirements for porous materials are becoming complicated and thus there are limitations in applying the existing porous metal and alloy materials to the above mentioned fields.
As an example of pore-containing metal, a metal porous body (WO 2003/070401) was recently disclosed. The metal porous body is prepared by fusing a metal alloy comprising iron, nickel, copper and the like and dissolving a gas into the fused metal material, followed by cooling. It is a lightweight iron material and has a tensile strength comparable to non-porous iron materials, as well as a high strength. Therefore, it is expected to substitute for iron. However, the preparation process and the setting of conditions for the preparation process are complicated, and thus, industrialization thereof is not easy.
Accordingly, the present inventors have made extensive efforts to develop a substitute for the existing heavyweight stainless steels, and studies and, as a result, confirmed that, when lightweight iron is prepared using metallic minerals, or a mixture of metallic materials and non-metallic materials, the weight of the lightweight iron can be decreased by adding diamond or silicon carbide to form pores inside the iron body, and a lightweight iron having desired properties and effects can be prepared by controlling sintering temperature and addition ratio of diamond or silicon carbide in the preparation process, thereby completing the present invention.